1. Field of the Invention
The present invention relates to an internal combustion engine with an altitude compensation device operative to automatically control the engine operation in accordance with the atmospheric air pressure which varies with the decrease and increase in the altitude at which a motor vehicle is placed.
2. Description of the Prior Art
It has been known to use an altitude compensation device operative to advance the ignition timing of an internal combustion engine when the atmospheric air pressure is decreased due to the increase in the altitude, to thereby compensate the output of the engine for the output power drop which would otherwise occur due to the decrease in the atmospheric air pressure. The prior art altitude compensation device for controlling the ignition timing advancer, however, is designed such that the ignition timing is contolled stepwise as the atmospheric pressure reaches predetermined levels. Thus, the ignition timing cannot be controlled continuously in accordance with the atmospheric pressure level at which the engine is operated.
It has also been known to use an altitude compensation device to control the air-fuel ratio of an air-fuel mixture produced by a carburetor. One type of the altitude compensation device comprises a set of solenoid valve and a duty cycle controlling circuit for controlling the ratio of the time periods while the solenoid valve is opened and closed, respectively. In general, a conventional carburetor is provided with a plurality of fuel circuits, such as main and slow circuits, and also with a power system. Thus, the altitude compensation means for a carburetor comprises a plurality of sets of solenoid valves and duty cycle controlling circuits. The prior art altitude compensation means for carburetor, therefore, are complicated in structure and increase the cost of manufacture of the carburetor.